Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
In the back-end manufacturing process, the wafers are commonly marked with a laser. The laser-marking may occur on the backside of the wafer to avoid damaging the active surface. The laser-marking can denote company logos and trademarks, identification of known good units, pin orientation, manufacturing history, lot number, time/date traceability, and component identification. For example, the marking can be used to facilitate traceability of the manufacturing process for fault analysis of semiconductor devices. The marking must be machine-readable, miniaturized and have no negative influence on the further manufacturing steps and still permit clear identification at the end of the process chain. The laser-marking can be numbers, letters, bar codes, dot matrix codes, and other identifying patterns and symbols.
In applications requiring both large bumps and thin wafers, wafer warpage or breakage is a recurring manufacturing issue in view of the bump height variation and stress of reflowing the large bumps on the thin wafer. The warped semiconductor wafers may have 0.8-1.0 millimeter (mm) variation across the surface.
Many laser-marking systems have difficulty processing wafers with a high degree of warping. When the wafer warpage reaches the range of 0.8-1.0 millimeter or above, the laser-marking machine encounters a vacuum error, as it cannot make a seal on the warped surface to pick up the wafer. In addition, the laser resolution degrades over the uneven warped surface. The laser-marking error interrupts the process flow, reduces yield, and increase manufacturing costs.